Receiver circuits for processing RF signals typically comprise some kind of amplifiers, e.g. at least one low-noise amplifier (LNA) to amplify a received signal while adding negligible noise. In particular with narrow band receivers, generally at least one or several LC tank circuits or LC resonator circuits are commonly used to remove noise as well as signals lying outside a frequency band of interest. Moreover, the gain and the center frequency of a low-noise amplifier (LNA) represent two critical parameters regarding the overall design of such amplifiers. Additionally, the gain of the low-noise amplifier (LNA) strongly depends on the voltage supply, the surrounding temperature and is further dependent on intrinsic or inherent individual properties of its electronic components.
Moreover, also the center frequency of a low-noise amplifier (LNA) depends on the concrete value of the capacitor and the inductor of the LC tank circuit. The center frequency therefore changes with temperature and strongly depends on inevitable variations of the manufacturing process. Hence, electronic components of the LC tank, in particular its capacitors and inductors, and the quality factor of the inductor are subject to non-negligible variance. The absolute capacitance of a series of substantially identical capacitors may vary up to 5%, 10% or even more. Moreover, under practical manufacturing conditions also the variance of a series of inductive elements may vary up to 5% regarding their absolute inductance, and the variation of the quality factor of the inductor with temperature, which can change by 10 to 20%.
It is therefore necessary to adjust the center frequency and the voltage gain of each narrow band amplifier or LNA in a narrow band receiver or transceiver individually in order to provide a desired receiver or transceiver performance. However, adjusting voltage gain and center frequency in a narrow band amplifier or LNA circuit is rather challenging and quite costly.
In FIG. 1, a conventional narrow band receiver 1 is illustrated. The receiver 1 comprises an antenna 2 coupled with an impedance matching circuit 3. The output of the impedance matching circuit 3 is provided to an amplifier 4, in particular to a LNA.
The output of the LNA 4 is coupled with a mixer 5. The narrow band receiver 1 also comprises a voltage controlled oscillator 7 coupled with the mixer 5. The output of the mixer 5 is typically provided to a filter and demodulator 6 for further processing the received signals.
Also the voltage controlled oscillator (VCO) requires proper adjustment of its center frequency and of its voltage swing. Therefore, the VCO is provided with a tuning loop 8, which may be implemented for example as a phase locked loop (PLL), and which can include also an amplitude locked loop (ALL) and/or a frequency locked loop (FLL). Said PLL is typically locked and controlled by a reference 9, e.g. comprising a crystal oscillating at a given reference frequency.
Conventional designs for narrow band receiver circuits comprise at least two control loops or mechanisms 10, 8 separately coupled to the amplifier 4 and to the VCO 7. The tuning and adjustment of the amplifier 4 and the VCO 7 therefore has to be typically performed separately. As a consequence, tuning of the amplifier's gain and center frequency is separated from a respective tuning of the VCO. Therefore, respective tuning procedures have to be conducted for the VCO and for the amplifier separately, thus raising tuning efforts and costs.